Butyl-bridged diphosphine ligands for alkoxycarbonylation

ABSTRACT

The invention relates to compounds of formula (I) 
     
       
         
         
             
             
         
       
         
         where
       R 1 , R 2 , R 3 , R 4  are each independently selected from —(C 1 -C 12 )-alkyl, —(C 3 -C 12 )-cycloalkyl, —(C 3 -C 12 )-heterocycloalkyl, —(C 6 -C 20 )-aryl, —(C 3 -C 20 )-heteroaryl;   
     
         at least one of the R 1 , R 2 , R 3 , R 4  radicals is a —(C 3 -C 20 )-heteroaryl radical; 
         and 
         R 1 , R 2 , R 3 , R 4 , if they are —(C 1 -C 12 )-alkyl, —(C 3 -C 12 )-cycloalkyl, —(C 3 -C 12 )-heterocycloalkyl, —(C 6 -C 20 )-aryl or —(C 3 -C 20 )-heteroaryl, 
         may each independently be substituted by one or more substituents selected from —(C 1 -C 12 )-alkyl, —(C 3 -C 12 )-cycloalkyl, —(C 3 -C 12 )-heterocycloalkyl, —O—(C 1 -C 12 )-alkyl, —O—(C 1 -C 12 )-alkyl-(C 6 -C 20 )-aryl, —O—(C 3 -C 12 )-cycloalkyl, —S—(C 1 -C 12 )-alkyl, —S—(C 3 -C 12 )-cycloalkyl, —COO—(C 1 -C 12 )-alkyl, —COO—(C 3 -C 12 )-cycloalkyl, —CONH—(C 1 -C 12 )-alkyl, —CONH—(C 3 -C 12 )-cycloalkyl, —CO—(C 1 -C 12 )-alkyl, —CO—(C 3 -C 12 )-cycloalkyl, —N—[(C 1 -C 12 )-alkyl] 2 , —(C 6 -C 20 )-aryl, —(C 6 -C 20 )-aryl-(C 1 -C 12 )-alkyl, —(C 6 -C 20 )-aryl-O—(C 1 -C 12 )-alkyl, —(C 3 -C 20 )-heteroaryl, —(C 3 -C 20 )-heteroaryl-(C 1 -C 12 )-alkyl, —(C 3 -C 20 )-heteroaryl-O-(C 1 -C 12 )-alkyl, —COOH, —OH, —SO 3 H, —NH 2 , halogen; 
         and to the use thereof as ligands in alkoxycarbonylation.

The invention relates to butyl-bridged diphosphine compounds, to metal complexes of these compounds and to the use thereof for alkoxycarbonylation.

The alkoxycarbonylation of ethylenically unsaturated compounds is a process of increasing significance. An alkoxycarbonylation is understood to mean the reaction of ethylenically unsaturated compounds (olefins) with carbon monoxide and alcohols in the presence of a metal-ligand complex to give the corresponding esters. Typically, the metal used is palladium. The following scheme shows the general reaction equation of an alkoxycarbonylation:

Among the alkoxycarbonylation reactions, particularly the reaction of ethene and methanol to give 3-methylpropionate (ethene methoxycarbonylation) is of significance as an intermediate step for the preparation of methyl methacrylate (S. G. Khokarale, E. J. Garcia-Suárez, J. Xiong, U. V. Mentzel, R. Fehrmann, A. Riisager, Catalysis Communications 2014, 44, 73-75). Ethene methoxycarbonylation is conducted in methanol as solvent under mild conditions with a palladium catalyst modified by phosphine ligands.

Typically, bidentate diphosphine compounds are used here as ligands. A very good catalytic system was developed by Lucite—now Mitsubishi Rayon—and uses a ligand based on 1,2-bis(di-tert-butylphosphinomethyl)benzene (DTBPMB) (W. Clegg, G. R. Eastham, M. R. J. Elsegood, R. P. Tooze, X. L. Wang, K. Whiston, Chem. Commun. 1999, 1877-1878).

EP 0975574 A1 discloses the carbonylation of 3-methoxy-1-butene to give methyl 3-pentenoate in the presence of, for example, 1,4-bis(diphenylphosphino)butane and 1,4-bis(dicyclohexylphosphino)butane. The carbonylation of long-chain ethylenically unsaturated compounds, such as octene for example, is not examined.

1,4-Bis(dialkylphosphino)butane compounds are also used in other sectors as ligands for palladium catalysts. For example, WO 02/10178 discloses the use of 1,4-bis(diadamantyl-phosphino)butane as a ligand for adding value to haloaromatics and for production of arylolefins, dienes, diaryls, benzoic acid and acrylic acid derivatives, arylalkanes and amines. However, there is no description of the use of these ligands for alkoxycarbonylation.

The problem addressed by the present invention is that of providing novel ligands for alkoxycarbonylation, with which good yields of esters can be achieved. More particularly, the ligands according to the invention are to be suitable for the alkoxycarbonylation of long-chain ethylenically unsaturated compounds, for example C₈ olefins, and of mixtures of ethylenically unsaturated compounds.

This problem is solved by butyl-bridged diphosphine compounds substituted by at least one heteroaryl radical on at least one phosphorus atom. These compounds are particularly suitable as bidentate ligands for palladium complexes and lead to elevated yields in the alkoxycarbonylation of ethylenically unsaturated compounds, especially of C₈ olefins.

The diphosphine compounds according to the invention are compounds of formula (I)

where

R¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl;

at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₂₀)-heteroaryl radical;

and

R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl,

may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl, —COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl, —CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl, —N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen.

The expression (C₁-C₁₂)-alkyl encompasses straight-chain and branched alkyl groups having 1 to 12 carbon atoms. These are preferably (C₁-C₈)-alkyl groups, more preferably (C₁-C₆)-alkyl, most preferably (C₁-C₄)-alkyl.

Suitable (C₁-C₁₂)-alkyl groups are especially methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1,3-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl, 3-heptyl, 2-ethylpentyl, 1-propylbutyl, n-octyl, 2-ethylhexyl, 2-propylheptyl, nonyl, decyl.

The elucidations relating to the expression (C₁-C₁₂)-alkyl also apply particularly to the alkyl groups in —O—(C₁-C₁₂)-alkyl, —S—(C₁-C₁₂)-alkyl, —COO—(C₁-C₁₂)-alkyl, —CONH—(C₁-C₁₂)-alkyl, —CO—(C₁-C₁₂)-alkyl and —N—[(C₁-C₁₂)-alkyl]₂.

The expression (C₃-C₁₂)-cycloalkyl encompasses mono-, bi- or tricyclic hydrocarbyl groups having 3 to 12 carbon atoms. Preferably, these groups are (C₅-C₁₂)-cycloalkyl.

The (C₃-C₁₂)-cycloalkyl groups have preferably 3 to 8, more preferably 5 or 6, ring atoms.

Suitable (C₃-C₁₂)-cycloalkyl groups are especially cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, cyclopentadecyl, norbomyl, adamantyl.

The elucidations relating to the expression (C₃-C₁₂)-cycloalkyl also apply particularly to the cycloalkyl groups in —O—(C₃-C₁₂)-cycloalkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₃-C₁₂)-cycloalkyl.

The expression (C₃-C₁₂)-heterocycloalkyl encompasses nonaromatic, saturated or partly unsaturated cycloaliphatic groups having 3 to 12 carbon atoms, where one or more of the ring carbon atoms are replaced by heteroatoms. The (C₃-C₁₂)-heterocycloalkyl groups have preferably 3 to 8, more preferably 5 or 6, ring atoms and are optionally substituted by aliphatic side chains. In the heterocycloalkyl groups, as opposed to the cycloalkyl groups, one or more of the ring carbon atoms are replaced by heteroatoms or heteroatom-containing groups. The heteroatoms or the heteroatom-containing groups are preferably selected from O, S, N, N(═O), C(═O), S(═O). A (C₃-C₁₂)-heterocycloalkyl group in the context of this invention is thus also ethylene oxide.

Suitable (C₃-C₁₂)-heterocycloalkyl groups are especially tetrahydrothiophenyl, tetrahydrofuryl, tetrahydropyranyl and dioxanyl.

The expression (C₆-C₂₀)-aryl encompasses mono- or polycyclic aromatic hydrocarbyl radicals having 6 to 20 carbon atoms. These are preferably (C₆-C₁₄)-aryl, more preferably (C₆-C₁₀)-aryl.

Suitable (C₆-C₂₀)-aryl groups are especially phenyl, naphthyl, indenyl, fluorenyl, anthracenyl, phenanthrenyl, naphthacenyl, chrysenyl, pyrenyl, coronenyl. Preferred (C₆-C₂₀)-aryl groups are phenyl, naphthyl and anthracenyl.

The expression (C₃-C₂₀)-heteroaryl encompasses mono- or polycyclic aromatic hydrocarbyl radicals having 3 to 20 carbon atoms, where one or more of the carbon atoms are replaced by heteroatoms. Preferred heteroatoms are N, O and S. The (C₃-C₂₀)-heteroaryl groups have 3 to 20, preferably 6 to 14 and more preferably 6 to 10 ring atoms. Thus, for example, pyridyl in the context of this invention is a C₆-heteroaryl radical; furyl is a C₅-heteroaryl radical.

Suitable (C₃-C₂₀)-heteroaryl groups are especially furyl, thienyl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, furazanyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidyl, pyrazinyl, benzofuranyl, indolyl, isoindolyl, benzimidazolyl, quinolyl, isoquinolyl.

The expression halogen especially encompasses fluorine, chlorine, bromine and iodine. Particular preference is given to fluorine and chlorine.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C12)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —O—(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl and —(C₃-C₂₀)-heteroaryl.

In one embodiment, the R¹, R², R³, R⁴ radicals are unsubstituted if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, or —(C₃-C₁₂)-heterocycloalkyl, and may be substituted as described if they are —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl.

In one embodiment, the R¹, R², R³, R⁴ radicals are unsubstituted if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl.

In one embodiment, R¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl;

where at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₂₀)-heteroaryl radical;

and R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more of the above-described substituents.

In a preferred embodiment, R¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl and —(C₃-C₂₀)-heteroaryl;

where at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₂₀)-heteroaryl radical;

and R¹, R², R³, R⁴ may each independently be substituted by one or more of the above-described substituents.

In one embodiment, at least two of the R¹, R², R³, R⁴ radicals are a —(C₃-C₂₀)-heteroaryl radical.

In one embodiment, the R¹ and R³ radicals are each a —(C₃-C₂₀)-heteroaryl radical and may each independently be substituted by one or more of the substituents described above. Preferably, R² and R⁴ are independently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, more preferably from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₆-C₂₀)-aryl, most preferably from —(C₁-C₁₂)-alkyl. R² and R⁴ may independently be substituted by one or more of the above-described substituents.

In one embodiment, the R¹, R², R³ and R⁴ radicals are a —(C₆-C₂₀)-heteroaryl radical and may each independently be substituted by one or more of the substituents described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are each independently selected from heteroaryl radicals having five to ten ring atoms, preferably five or six ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are a heteroaryl radical having five ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are each independently selected from heteroaryl radicals having six to ten ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are a heteroaryl radical having six ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are selected from furyl, thienyl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, furazanyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidyl, pyrazinyl, benzofuranyl, indolyl, isoindolyl, benzimidazolyl, quinolyl, isoquinolyl, where the heteroaryl radicals mentioned may be substituted as described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are selected from furyl, thienyl, pyrrolyl, imidazolyl, pyridyl, pyrimidyl, indolyl, where the heteroaryl radicals mentioned may be substituted as described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are selected from 2-furyl, 2-thienyl, 2-pyrrolyl, 2-imidazolyl, 2-pyridyl, 2-pyrimidyl, 2-indolyl, where the heteroaryl radicals mentioned may be substituted as described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are selected from 2-furyl, 2-thienyl, N-methyl-2-pyrrolyl, N-phenyl-2-pyrrolyl, N-(2-methoxyphenyl)-2-pyrrolyl, 2-pyrrolyl, N-methyl-2-imidazolyl, 2-imidazolyl, 2-pyridyl, 2-pyrimidyl, N-phenyl-2-indolyl, 2-indolyl, where the heteroaryl radicals mentioned have no further substitution.

More preferably, the R¹, R², R³ and R⁴ radicals, if they are a heteroaryl radical, are pyridyl, especially 2-pyridyl.

In one embodiment, R¹ and R³ are a pyridyl radical, preferably 2-pyridyl, and R² and R⁴ are —(C₁-C₁₂)-alkyl, where R¹, R², R³ and R⁴ may each be substituted as described above.

In one embodiment, the diphosphine compounds according to the invention are a compound of formula (1):

The invention further relates to complexes comprising Pd and a diphosphine compound according to the invention. In these complexes, the diphosphine compound according to the invention serves as a bidentate ligand for the metal atom. The complexes serve, for example, as catalysts for alkoxycarbonylation. With the complexes according to the invention, it is possible to achieve high yields in the alkoxycarbonylation of a multitude of different ethylenically unsaturated compounds.

The complexes according to the invention may also comprise further ligands which coordinate to the metal atom. These are, for example, ethylenically unsaturated compounds or anions. Suitable additional ligands are, for example, styrene, acetate anions, maleimides (e.g. N-methylmaleimide), 1,4-naphthoquinone, trifluoroacetate anions or chloride anions.

The invention further relates to the use of a diphosphine compound according to the invention for catalysis of an alkoxycarbonylation reaction. The compound according to the invention can especially be used as a metal complex according to the invention.

The invention also relates to a process comprising the process steps of:

-   -   a) initially charging an ethylenically unsaturated compound;     -   b) adding a diphosphine compound according to the invention and         a compound comprising Pd,         -   or adding a complex according to the invention comprising Pd             and a diphosphine compound according to the invention;     -   c) adding an alcohol;     -   d) feeding in CO;     -   e) heating the reaction mixture, with conversion of the         ethylenically unsaturated compound to an ester.

In this process, process steps a), b), c) and d) can be effected in any desired sequence. Typically, however, the addition of CO is effected after the co-reactants have been initially charged in steps a) to c). Steps d) and e) can be effected simultaneously or successively. In addition, CO can also be fed in in two or more steps, in such a way that, for example, a portion of the CO is first fed in, then the mixture is heated, and then a further portion of CO is fed in.

The ethylenically unsaturated compounds used as reactant in the process according to the invention contain one or more carbon-carbon double bonds. These compounds are also referred to hereinafter as olefins for simplification. The double bonds may be terminal or internal.

Preference is given to ethylenically unsaturated compounds having 2 to 30 carbon atoms, preferably 2 to 22 carbon atoms, more preferably 2 to 12 carbon atoms.

In one embodiment, the ethylenically unsaturated compound comprises 4 to 30 carbon atoms, preferably 6 to 22 carbon atoms, more preferably 8 to 12 carbon atoms. In a particularly preferred embodiment, the ethylenically unsaturated compound comprises 8 carbon atoms.

The ethylenically unsaturated compounds may, in addition to the one or more double bonds, contain further functional groups. Preferably, the ethylenically unsaturated compound comprises one or more functional groups selected from carboxyl, thiocarboxyl, sulpho, sulphinyl, carboxylic anhydride, imide, carboxylic ester, sulphonic ester, carbamoyl, sulphamoyl, cyano, carbonyl, carbonothioyl, hydroxyl, sulphhydryl, amino, ether, thioether, aryl, heteroaryl or silyl groups and/or halogen substituents. At the same time, the ethylenically unsaturated compound preferably comprises a total of 2 to 30 carbon atoms, preferably 2 to 22 carbon atoms, more preferably 2 to 12 carbon atoms.

In one embodiment, the ethylenically unsaturated compound does not comprise any further functional groups apart from carbon-carbon double bonds.

In a particularly preferred embodiment, the ethylenically unsaturated compound is an unfunctionalized alkene having at least one double bond and 2 to 30 carbon atoms, preferably 6 to 22 carbon atoms, further preferably 8 to 12 carbon atoms, and most preferably 8 carbon atoms.

Suitable ethylenically unsaturated compounds are, for example:

-   -   ethene;     -   propene;     -   C4 olefins such as 1-butene, cis-2-butene, trans-2-butene,         mixture of cis- and trans-2-butene, isobutene, 1,3-butadiene;         raffinate I to III, crack-C4     -   C5 olefins such as 1-pentene, 2-pentene, 2-methyl-1-butene,         2-methyl-2-butene, 2-methyl-1,3-butadiene (isoprene),         1,3-pentadiene;     -   C6 olefins such as tetramethylethylene, 1,3-hexadiene,         1,3-cyclohexadiene;     -   C7 olefins such as 1-methylcyclohexene, 2,4-heptadiene,         norbornadiene;     -   C8 olefins such as 1-octene, 2-octene, cyclooctene, di-n-butene,         diisobutene, 1,5-cyclooctadiene, 1,7-octadiene;     -   C9 olefins such as tripropene;     -   C10 olefins such as dicyclopentadiene;     -   undecenes;     -   dodecenes;     -   internal C14 olefins;     -   internal C15 to C18 olefins;     -   linear or branched, cyclic, acyclic or partly cyclic, internal         C15 to C30 olefins;     -   triisobutene, tri-n-butene;     -   terpenes such as limonene, geraniol, farnesol, pinene, myrcene,         carvone, 3-carene;     -   polyunsaturated compounds having 18 carbon atoms, such as         linoleic acid or linolenic acid;     -   esters of unsaturated carboxylic acids, such as vinyl esters of         acetic or propionic acid, alkyl esters of unsaturated carboxylic         acids, methyl or ethyl esters of acrylic acid and methacrylic         acid, oleic esters, such as methyl or ethyl oleate, esters of         linoleic or linolenic acid;     -   vinyl compounds such as vinyl acetate, vinylcyclohexene,         styrene, alpha-methylstyrene, 2-isopropenylnaphthalene;     -   2-methyl-2-pentenal, methyl 3-pentenoate, methacrylic anhydride.

In one variant of the process, the ethylenically unsaturated compound is selected from propene, 1-butene, cis- and/or trans-2-butene, or mixtures thereof.

In one variant of the process, the ethylenically unsaturated compound is selected from 1-pentene, cis- and/or trans-2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, or mixtures thereof.

In a preferred embodiment, the ethylenically unsaturated compound is selected from ethene, propene, 1-butene, cis- and/or trans-2-butene, isobutene, 1,3-butadiene, 1-pentene, cis- and/or trans-2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, hexene, tetramethylethylene, heptene, n-octene, 1-octene, 2-octene, or mixtures thereof.

In one variant, a mixture of ethylenically unsaturated compounds is used. A mixture in the context of this invention refers to a composition comprising at least two different ethylenically unsaturated compounds, where the proportion of each individual ethylenically unsaturated compound is preferably at least 5% by weight, based on the total weight of the mixture.

Preference is given to using a mixture of ethylenically unsaturated compounds each having 2 to 30 carbon atoms, preferably 4 to 22 carbon atoms, more preferably 6 to 12 carbon atoms, most preferably 8 to 10 carbon atoms.

Suitable mixtures of ethylenically unsaturated compounds are those called raffinates I to III. Raffinate I comprises 40% to 50% isobutene, 20% to 30% 1-butene, 10% to 20% cis- and trans-2-butene, up to 1% 1,3-butadiene and 10% to 20% n-butane and isobutane. Raffinate II is a portion of the C₄ fraction which arises in naphtha cracking and consists essentially of the isomeric n-butenes, isobutane and n-butane after removal of isobutene from raffinate I. Raffinate III is a portion of the C₄ fraction which arises in naphtha cracking and consists essentially of the isomeric n-butenes and n-butane.

A further suitable mixture is di-n-butene, also referred to as dibutene, DNB or DnB. Di-n-butene is an isomer mixture of C8 olefins which arises from the dimerization of mixtures of 1-butene, cis-2-butene and trans-2-butene. In industry, raffinate II or raffinate III streams are generally subjected to a catalytic oligomerization, wherein the butanes present (n/iso) emerge unchanged and the olefins present are converted fully or partly. As well as dimeric di-n-butene, higher oligomers (tributene C12, tetrabutene C16) generally also form, which are removed by distillation after the reaction. These can likewise be used as reactants.

In a preferred variant, a mixture comprising isobutene, 1-butene, cis- and trans-2-butene is used. Preferably, the mixture comprises 1-butene, cis- and trans-2-butene.

The alkoxycarbonylation according to the invention is catalysed by the Pd complex according to the invention. The Pd complex may either be added in process step b) as a preformed complex comprising Pd and the phosphine ligands according to the invention or be formed in situ from a compound comprising Pd and the free phosphine ligand. In this context, the compound comprising Pd is also referred to as catalyst precursor.

In the case that the catalyst is formed in situ, the ligand can be added in excess, such that the unbound ligand is also present in the reaction mixture.

In one variant, the compound comprising Pd is selected from palladium chloride (PdCl₂), palladium(II) acetylacetonate [Pd(acac)₂], palladium(II) acetate [Pd(OAc)₂], dichloro(1,5-cyclooctadiene)palladium(II) [Pd(cod)₂Cl₂], bis(dibenzylideneacetone)palladium [Pd(dba)₂], bis(acetonitrile)dichloropalladium(ll) [Pd(CH₃CN)₂Cl₂], palladium(cinnamyl) dichloride [Pd(cinnamyl)Cl₂].

Preferably, the compound comprising Pd is PdCl₂, Pd(acac)₂ or Pd(OAc)₂. PdCl₂ is particularly suitable.

The alcohol in process step c) may be branched or linear, cyclic, alicyclic, partly cyclic or aliphatic, and is especially a C₁- to C₃₀-alkanol. It is possible to use monoalcohols or polyalcohols.

The alcohol in process step c) comprises preferably 1 to 30 carbon atoms, more preferably 1 to 22 carbon atoms, especially preferably 1 to 12 carbon atoms. It may be a monoalcohol or a polyalcohol.

The alcohol may, in addition to the one or more hydroxyl groups, contain further functional groups. Preferably, the alcohol may additionally comprise one or more functional groups selected from carboxyl, thiocarboxyl, sulpho, sulphinyl, carboxylic anhydride, imide, carboxylic ester, sulphonic ester, carbamoyl, sulphamoyl, cyano, carbonyl, carbonothioyl, sulphhydryl, amino, ether, thioether, aryl, heteroaryl or silyl groups and/or halogen substituents.

In one embodiment, the alcohol does not comprise any further functional groups except for hydroxyl groups.

The alcohol may contain unsaturated and aromatic groups. However, it is preferably an aliphatic alcohol.

An aliphatic alcohol in the context of this invention refers to an alcohol which does not comprise any aromatic groups, i.e., for example, an alkanol, alkenol or alkynol. Unsaturated nonaromatic alcohols are thus also permitted.

In one embodiment, the alcohol is an alkanol having one or more hydroxyl groups and 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, more preferably 1 to 12 carbon atoms, most preferably 1 to 6 carbon atoms.

In one variant of the process, the alcohol in process step c) is selected from the group of the monoalcohols.

In one variant of the process, the alcohol in process step c) is selected from: methanol, ethanol, 1-propanol, isopropanol, isobutanol, tert-butanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, cyclohexanol, phenol, 2-ethylhexanol, isononanol, 2-propylheptanol.

In a preferred variant, the alcohol in process step c) is selected from methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 2-propanol, tert-butanol, 3-pentanol, cyclohexanol, phenol, and mixtures thereof.

In one variant of the process, the alcohol in process step c) is selected from the group of the polyalcohols.

In one variant of the process, the alcohol in process step c) is selected from: diols, triols, tetraols.

In one variant of the process, the alcohol in process step c) is selected from: cyclohexane-1,2-diol, ethane-1,2-diol, propane-1,3-diol, glycerol, butane-1,2,4-triol, 2-hydroxymethylpropane-1,3-diol, 1,2,6-trihydroxyhexane, pentaerythritol, 1,1,1-tri(hydroxymethyl)ethane, catechol, resorcinol and hydroxyhydroquinone.

In one variant of the process, the alcohol in process step c) is selected from: sucrose, fructose, mannose, sorbose, galactose and glucose.

In a preferred embodiment of the process, the alcohol in process step c) is selected from methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol.

In a particularly preferred variant of the process, the alcohol in process step c) is selected from: methanol, ethanol.

In a particularly preferred variant of the process, the alcohol in process step c) is methanol.

In one variant of the process, the alcohol in process step c) is used in excess.

In one variant of the process, the alcohol in process step c) is used simultaneously as solvent.

In one variant of the process, a further solvent is used, selected from: toluene, xylene, tetrahydrofuran (THF) and methylene chloride (CH₂Cl₂).

CO is fed in in step d) preferably at a partial CO pressure between 0.1 and 10 MPa (1 to 100 bar), preferably between 1 and 8 MPa (10 to 80 bar), more preferably between 2 and 4 MPa (20 to 40 bar).

The reaction mixture is heated in step e) of the process according to the invention preferably to a temperature between 10° C. and 180° C., preferably between 20 and 160° C., more preferably between 40 and 120° C., in order to convert the ethylenically unsaturated compound to an ester.

The molar ratio of the ethylenically unsaturated compound initially charged in step a) to the alcohol added in step c) is preferably between 1:1 and 1:20, more preferably 1:2 to 1:10, more preferably 1:3 to 1:4.

The mass ratio of Pd to the ethylenically unsaturated compound initially charged in step a) is preferably between 0.001% and 0.5% by weight, preferably between 0.01% and 0.1% by weight, more preferably between 0.01% and 0.05% by weight.

The molar ratio of the diphosphine compound according to the invention to Pd is preferably between 0.1:1 and 400:1, preferably between 0.5:1 and 400:1, more preferably between 1:1 and 100:1, most preferably between 2:1 and 50:1.

Preferably, the process is conducted with addition of an acid. In one variant, the process therefore additionally comprises step c′): adding an acid to the reaction mixture. This may preferably be a Brønsted or Lewis acid.

Suitable Brønsted acids preferably have an acid strength of pK_(a)≧5, preferably an acid strength of pK_(a)≧3. The reported acid strength pK_(a) is based on the pK_(a) determined under standard conditions (25° C., 1.01325 bar). In the case of a polyprotic acid, the acid strength pK_(a) in the context of this invention relates to the pK_(a) of the first protolysis step.

Preferably, the acid is not a carboxylic acid.

Suitable Brønsted acids are, for example, perchloric acid, sulphuric acid, phosphoric acid, methylphosphonic acid and sulphonic acids. Preferably, the acid is sulphuric acid or a sulphonic acid. Suitable sulphonic acids are, for example, methanesulphonic acid, trifluoromethanesulphonic acid, tert-butanesulphonic acid, p-toluenesulphonic acid (PTSA), 2-hydroxypropane-2-sulphonic acid, 2,4,6-trimethylbenzenesulphonic acid and dodecylsulphonic acid. Particularly preferred acids are sulphuric acid, methanesulphonic acid, trifluoromethanesulphonic acid and p-toluenesulphonic acid.

A Lewis acid used may, for example, be aluminium triflate.

In one embodiment, the amount of acid added in step c′) is 0.3 to 40 mol %, preferably 0.4 to 15 mol %, more preferably 0.5 to 5 mol %, most preferably 0.6 to 3 mol %, based on the molar amount of the ethylenically unsaturated compound used in step a).

EXAMPLES

The examples which follow illustrate the invention.

General Procedures

All the preparations which follow were carried out under protective gas using standard Schlenk techniques. The solvents were dried over suitable desiccants before use (Purification of Laboratory Chemicals, W. L. F. Armarego (Author), Christina Chai (Author), Butterworth Heinemann (Elsevier), 6th edition, Oxford 2009).

Phosphorus trichloride (Aldrich) was distilled under argon before use. All preparative operations were effected in baked-out vessels. The products were characterized by means of NMR spectroscopy. Chemical shifts (δ) are reported in ppm. The ³¹P NMR signals were referenced as follows: SR_(31P)═SR_(1H)*(BF_(31P)/BF_(1H))═SR_(1H)*0.4048. (Robin K. Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Robin Goodfellow, and Pierre Granger, Pure Appl. Chem., 2001, 73, 1795-1818; Robin K. Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Pierre Granger, Roy E. Hoffman and Kurt W. Zilm, Pure Appl. Chem., 2008, 80, 59-84).

The recording of nuclear resonance spectra was effected on Bruker Avance 300 or Bruker Avance 400, gas chromatography analysis on Agilent GC 7890A, elemental analysis on Leco TruSpec CHNS and Varian ICP-OES 715, and ESI-TOF mass spectrometry on Thermo Electron Finnigan MAT 95-XP and Agilent 6890 N/5973 instruments.

Preparation of chloro-2-pyridyl-tert-butylphosphine (Precursor A)

The Grignard for the synthesis of chloro-2-pyridyl-t-butylphosphine is prepared by the “Knochel method” with isopropylmagnesium chloride (Angew. Chem. 2004, 43, 2222-2226). The workup is effected according to the method of Budzelaar (Organometallics 1990, 9, 1222-1227).

8.07 ml of a 1.3 M isopropylmagnesium chloride solution (Knochel's reagent) are introduced into a 50 ml round-bottom flask with magnetic stirrer and septum, and cooled to −15° C. Thereafter, 953.5 μl (10 mmol) of 2-bromopyridine are rapidly added dropwise. The solution immediately turns yellow. It is allowed to warm up to −10° C. The conversion of the reaction is determined as follows: about 100 μl solution are taken and introduced into 1 ml of a saturated ammonium chloride solution. If the solution “bubbles”, not much Grignard has formed yet. The aqueous solution is extracted with a pipette of ether and the organic phase is dried over Na₂SO₄. A GC of the ethereal solution is recorded. When a large amount of pyridine has formed compared to 2-bromopyridine, conversions are high. At −10° C., there has been little conversion. After warming up to room temperature and stirring for 1-2 hours, the reaction solution turns brown-yellow. A GC test shows complete conversion. Now the Grignard solution can be slowly added dropwise with a syringe pump to a solution of 1.748 g (11 mmol) of dichloro-tert-butylphosphine in 10 ml of THF which has been cooled to −15° C. beforehand. It is important that the dichloro-tert-butylphosphine solution is cooled. At room temperature, considerable amounts of dipyridyl-tert-butylphosphine would be obtained. A clear yellow solution is initially formed, which then turns cloudy. The mixture is left to warm up to room temperature and to stir overnight. According to GC-MS, a large amount of product has formed. The solvent is removed under high vacuum and a whitish solid which is brown in places is obtained. The solid is suspended with 20 ml of heptane and the solid is comminuted in an ultrasound bath. After allowing the white solid to settle out, the solution is decanted. The operation is repeated twice with 10-20 ml each time of heptane. After concentration of the heptane solution under high vacuum, it is distilled under reduced pressure. At 4.6 mbar, oil bath 120° C. and distillation temperature 98° C., the product can be distilled. 1.08 g of a colourless oil are obtained. (50%).

Analytical data: ¹H NMR (300 MHz, C₆D₆): δ 8.36 (m, 1H, Py), 7.67 (m, 1H, Py), 7.03-6.93 (m, 1H, Py), 6.55-6.46 (m, 1H, Py), 1.07 (d, J=13.3 Hz, 9H, t-Bu).

¹³C NMR (75 MHz, C₆D₆): δ 6 162.9, 162.6, 148.8, 135.5, 125.8, 125.7, 122.8, 35.3, 34.8, 25.9 and 25.8.

³¹P NMR (121 MHz, C₆D₆) δ 97.9.

MS (El) m:z (relative intensity) 201 (M⁺,2), 147 (32), 145 (100), 109 (17), 78 (8), 57.1 (17).

Preparation of Compound 1

675 mg (27.8 mmol, 4 equivalents) of Mg powder are weighed out in a glovebox in a 250 ml round-bottom flask with a nitrogen tap and magnetic stirrer bar, and the flask is sealed with a septum. High vacuum is applied to the round-bottom flask (about 5×10⁻² mbar) and it is heated to 90° C. for 45 minutes. After cooling down to room temperature, 2 grains of iodine are added and the mixture is dissolved in 20 ml of THF. The suspension is stirred for about 10 minutes until the yellow colour of the iodine has disappeared. After the magnesium powder has settled out, the cloudy THF solution is decanted and the activated magnesium powder is washed twice with 1-2 ml of THF. Then another 20 ml of fresh THF are added. At room temperature, a solution of 755.5 μl (6.9 mmol) of 1,4-dichlorobutane in 70 ml of THF is slowly added dropwise with a syringe pump. The THF solution is clear and pale yellow. The next day, the solution is dark grey but clear and is filtered through Celite. A sample of the Grignard solution is quenched and examined in GC as follows:

300 μl of Grignard solution is quenched with 1 ml of a saturated aqueous solution of NH₄Cl and extracted with ether. After drying over Na₂SO₄, a GC of the ether solution is recorded. 1,4-Dichlorobutane is no longer detectable, but the butane formed cannot be observed in the GC.

The content of Grignard compound is determined as follows:

1 ml of Grignard solution is quenched with 3 ml of 0.1 M HCl and the excess acid is titrated with 0.1 M NaOH. A suitable indicator is an aqueous 0.04% bromocresol solution. The colour change goes from yellow to blue. 1.70 ml of 0.1 M NaOH has been consumed. 3 ml−1.70 ml=1.3 ml, corresponding to 0.13 mmol of Grignard compound. Since a di-Grignard is present, the Grignard solution is 0.065 M.

Based on 90 ml of solution this is 85% of Grignard solution. The Grignard can now be reacted with the chlorophosphine:

In a 250 ml three-neck flask with reflux condenser, magnetic stirrer bar and nitrogen tap, under argon, 1.94 g (9.75 mmol, 2.5 eq) of chloro-2-pyridyl-t-butylphosphine (precursor A) are dissolved in 10 ml of THF and cooled to −60° C. Then 60 ml of the above-stipulated Grignard solution (0.065 M, 3.9 mmol) are slowly added dropwise at this temperature with a syringe pump. The solution at first remains clear and then turns intense yellow. The mixture is left to warm up to room temperature overnight and a clear yellow solution is obtained. To complete the reaction, the mixture is heated under reflux for 2 hours. After cooling, 1 ml of H₂O is added and the solution loses colour and a white solid precipitates out. After removing THF under high vacuum, a stringy, pale yellow solid is obtained. 15 ml of water and 20 ml of ether are added thereto, and two homogeneous clear phases are obtained, which have good separability. The aqueous phase is extracted twice with ether. After the organic phase has been dried with Na₂SO₄, the ether is removed under high vacuum and a viscous, almost colourless oil is obtained. The latter is dissolved in 4 ml of MeOH while heating on a water bath and filtered through Celite. At −28° C., 660 mg of product are obtained in the form of white tacky crystals overnight. (44%).

¹H NMR (300 MHz, C₆D₆): δ 8.54 (m, 2H, py), 7.37 (m, 2H, py), 6.96 (m, 2H, Py), 6.58 (m, 2H, Py), 2.68 (m, 2H, CH₂), 1.74 (m, 4H, CH₂), 1.52 (m; 2H, CH₂), 1.03 (d, J=11.5 Hz, 18H, tBu).

¹³C NMR (75 MHz, C₆D₆): δ 6 162.8, 162.5 (q), 149.9, 134.3, 134.1, 132.0, 131.5 and 122.4 (py), 29.4, 29.3, 29.1, 29.0, 20.7, 20.5 (CH₂), 28.1 and 27.9 (tBu).

³¹P NMR (121 MHz, C₆D₆) δ 8.2.

HRMS (ESI) m/z⁺ calculated for: C₂₂H₃₄N₂P₂ (M+H)⁺ 389.227; found: 389.2273. EA calculated for: C₂₂H₃₄N₂P₂: C, 68.02; H, 8.82; N, 7.21; P,15.95. found: C, 68.16; H, 8.97; N, 7.07; P,15.91.

Preparation of bis(diadamantylphosphinbutane borane adduct) (Precursor B)

In a 100 ml round-bottom flask with nitrogen tap and magnetic stirrer bar, 214.7 mg (0.679 mmol) of diadamantylphosphine borane adduct are weighed out. The flask is closed with a septum and, after purging with argon, 10 ml of THF are added. The borane adduct has good solubility in THF, and a clear colourless solution is obtained, which is cooled to −78° C. with dry ice. After stirring for 15 minutes, 0.5 ml (0.70 mmol) of a 1.4 M sec-BuLi solution is slowly added dropwise. After the dropwise addition, a pale yellowish, clear solution is obtained, which is brought to room temperature within 3 hours. The still pale yellowish solution is left to stir at room temperature for a further hour and the solution is cooled back to −78° C. Then 42.6 μl (0.323 mmol) of diiodobutane diluted with 5 ml of THF are slowly added dropwise to this solution. The yellow solution loses colour in the process. The mixture is left to warm up overnight, and a large amount of white solid precipitates out. 8 ml of water are added and the mixture is stirred vigorously for 20 minutes. Further solid floats on top of the solution. The solution is decanted and the white solid is washed three times with MeOH in order to remove any water still present. After drying under reduced pressure, a yield of 210 mg (95%) of a white solid is obtained.

¹H NMR (300 MHz, CDCl₃): δ 2.11-1.89 (m, 36H, Ad), 1.79-1.68 (m, 24H, Ad), 1.67-1.49 (m, 8H, CH₂), 1.03-(−0.51) (m, broad), 6H, BH₃).

¹³C NMR (75 MHz, CDCl₃): δ 37.8 and 36.6 (Ad), 36.5 and 36.4 (C), 28.1 and 28.0 (Ad), 27.9, 27.7, 15.1 and 14.7 ((CH₂)₄).

³¹P NMR (121 MHz, CDCl₃) δ 6 36.6-33.4 (m).

Preparation of diadamantylphosphine borane adduct (Precursor C)

4.0 g (13.22 mmol) of diadamantylphosphine are weighed out in a 100 ml round bottom flask with nitrogen tap and oval magnetic stirrer bar, closed with a septum and purged. The solid is suspended in 9 ml of THF and 18.9 ml (18.9 mmol, 1 M) of BH₃·THF adduct are added rapidly to this suspension. The suspension at first begins to dissolve. After a while, however, a white solid precipitates out. The mixture is left to stir overnight and the THF is removed under high vacuum. The white residue is taken up in 250 ml of ethyl acetate while heating (60° C.) on a water bath. The borane adduct has good solubility in the warm ethyl acetate. After addition of 6 spoonfuls of silica gel 60 (about 12 g), the solvent is removed completely on a rotary evaporator and the product which has been absorbed on silica gel is chromatographed with a Combi-Flash apparatus. The eluent used is 1:10 (ethyl acetate/heptane). 3.1 g (74%) of diadamantylphosphine borane adduct are obtained.

¹H NMR (300 MHz, CDCl₃): δ 6 3.71 (dq, 350.8 Hz and 6.6 Hz, 1H, PH), 2.01-1.94 (m, 18H, Ad), 1.74 (m, 12H, Ad), 1.05-(−0.35) (m, 3H, BH₃).

¹³C NMR (75 MHz, CDCl₃): δ 37.9 and 36.4 (CH₂), 34.8 and 34.4 (C), 28.1 and 28.0 (CH).

³¹P NMR (121 MHz, CDCl₃) δ 42.8-40.0 (m).

Preparation of Ligand 2: bis(diadamantylphosphino)butane (Comparative Ligand)

500 mg (0.728 mmol) of borane adduct are weighed out in a 25 ml round-bottom flask with nitrogen tap, and 10 ml of absolute pyrrolidine are added. The suspension is heated under reflux until the solution is colourless and clear (about 2 h). After cooling, the pyrrolidine is removed under high vacuum and a white residue was obtained. This is taken up in 15 ml of toluene and heated to 90° C. The almost clear solution is difficult to filter, since the product precipitates out again in the course of cooling. A white crystalline solid precipitates out of the filtrate in the refrigerator (3° C.). Crystals are washed twice with toluene and dried under high vacuum. 300 mg (62%) of white crystals are obtained.

Owing to poor solubility at room temperature, a 1H, 13C and 31P NMR in benzene-d6 is recorded at 323 K.

¹H NMR (323 K, 400 MHz, C₆D₆): δ 2.12-1.92 (m, 16H, CH₂, Ad), 1.92-1.79 (m, 11H, CH₂, Ad), 1.75-1.64 (m, 16H, CH₂, Ad), 1.64-1.47 (m, 6H, CH₂, Ad), 1.45-1.23 (m, 18H, CH₂, Ad).

¹³C NMR (323 K, 100 MHz, C₆D₆): δ 41.5 and 41.4 (Ad), 37.5 (Ad), 36.5 and 36.3 (C), 30.1 (CH₂), 29.3 and 29.2 (Ad), 17.5 and 17.3 (CH₂).

³¹P NMR (323 K, 162 MHz, C₆D₆) δ 25.71.

High-Pressure Experiments

Feedstocks:

Di-n-butene was also referred to as follows: dibutene, DNB or DnB.

Di-n-butene is an isomer mixture of C8 olefins which arises from the dimerization of mixtures of 1-butene, cis-2-butene and trans-2-butene. In industry, raffinate II or raffinate III streams are generally subjected to a catalytic oligomerization, wherein the butanes present (n/iso) emerge unchanged and the olefins present are converted fully or partly. As well as dimeric di-n-butene, higher oligomers (tributene C12, tetrabutene C16) generally also form, which have to be removed by distillation after the reaction.

Another process practised in industry for oligomerization of C4 olefins is called the “OCTOL process”.

Within the patent literature, DE102008007081A1, for example, describes an oligomerization based on the OCTOL process. EP1029839A1 is concerned with the fractionation of the C8 olefins formed in the OCTOL process.

Technical di-n-butene consists generally to an extent of 5% to 30% of n-octenes, 45% to 75% of 3-methylheptenes, and to an extent of 10% to 35% of 3,4-dimethylhexenes. Preferred streams contain 10% to 20% n-octenes, 55% to 65% 3-methylheptenes, and 15% to 25% 3,4-dimethylhexenes.

para-Toluenesulphonic acid was abbreviated as follows: pTSA, PTSA or p-TSA. PTSA in this text always refers to para-toluenesulphonic acid monohydrate.

General Method for Performance of the High-Pressure Experiments

General Experimental Method for Autoclave Experiments in Glass Vials:

A 300 ml Parr reactor is used. Matched to this is an aluminium block of corresponding dimensions which has been manufactured in-house and which is suitable for heating by means of a conventional magnetic stirrer, for example from Heidolph. For the inside of the autoclave, a round metal plate of thickness about 1.5 cm was manufactured, containing 6 holes corresponding to the external diameter of the glass vials. Matching these glass vials, they are equipped with small magnetic stirrers. These glass vials are provided with screw caps and suitable septa and charged, using a special apparatus manufactured by glass blowers, under argon with the appropriate reactants, solvents and catalysts and additives. For this purpose, 6 vessels are filled at the same time; this enables the performance of 6 reactions at the same temperature and the same pressure in one experiment. Then these glass vessels are closed with screw caps and septa, and a small syringe cannula of suitable size is used to puncture each of the septa. This enables gas exchange later in the reaction. These vials are then placed in the metal plate and these are transferred into the autoclave under argon. The autoclave is purged with CO and filled at room temperature with the CO pressure intended. Then, by means of the magnetic stirrer, under magnetic stirring, the autoclave is heated to reaction temperature and the reaction is conducted for the appropriate period. Subsequently, the autoclave is cooled down to room temperature and the pressure is slowly released. Subsequently, the autoclave is purged with nitrogen. The vials are taken from the autoclave, and a defined amount of a suitable standard is added. A GC analysis is effected, the results of which are used to determine yields and selectivities.

Analysis

GC analysis of di-n-butene: for the GC analysis, an Agilent 7890A gas chromatograph having a 30 m HP5 column is used. Temperature profile: 35° C., 10 min; 10° C./min to 200° C.; the injection volume is 1 μl with a split of 50:1.

Retention times for di-n-butene and products: 10.784-13.502 min

The esters formed from di-n-butene are referred to hereinafter as MINO (methyl isononanoate).

Retention time for ether products of unknown isomer distribution: 15.312, 17.042, 17.244, 17.417 min

Retention time for iso-C9 esters 19.502-20.439 min (main peak: 19.990 min)

Retention time for n-C9 esters: 20.669, 20.730, 20.884, 21.266 min.

Evaluation of the Experiments

For the evaluation of the catalytic experiments, particular indicators which permit comparison of the various catalyst systems are used hereinafter.

TON: turnover number, defined as moles of product per mole of catalyst metal, is a measure of the productivity of the catalytic complex.

TOF: turnover frequency, defined as TON per unit time for the attainment of a particular conversion, e.g. 50%. The TOF is a measure of the activity of the catalytic system.

The n selectivities reported hereinafter relate to the proportion of terminal methoxycarbonylation based on the overall yield of methoxycarbonylation products.

The n/iso ratio indicates the ratio of olefins converted terminally to esters to olefins converted internally to esters.

Methoxycarbonylation of di-n-butene

Ligand 2 (comparative example): A 25 ml Schlenk vessel was charged with a stock solution of [Pd(acac)₂] (1.95 mg, 6.4 μmol), p-toluenesulphonic acid (PTSA) (18.24 mg, 95.89 μmol) and MeOH (10 ml). A 4 ml vial was charged with 2 (2.11 mg, 0.16 mol % based on the molar amount of di-n-butene), and a magnetic stirrer bar was added. Thereafter, 1.25 ml of the clear yellow stock solution and di-n-butene (315 μl, 2 mmol) were added with a syringe. The molar proportions based on the molar amount of di-n-butene are thus 0.04 mol % for Pd(acac)₂ and 0.6 mol % for PTSA. The vial was placed into a sample holder which was in turn inserted into a 300 ml Parr autoclave under an argon atmosphere. After the autoclave had been purged three times with nitrogen, the CO pressure was adjusted to 40 bar. The reaction proceeded at 120° C. for 20 hours. On conclusion of the reaction, the autoclave was cooled down to room temperature and cautiously decompressed. Isooctane was added as internal GC standard. Yield and regioselectivity were determined by means of GC. No MINO formation was observed.

Ligand 1: A 25 ml Schlenk vessel was charged with a stock solution of [Pd(acac)₂] (1.95 mg, 6.4 μmol), p-toluenesulphonic acid (PTSA) (18.24 mg, 95.89 μmol) and MeOH (10 ml). A 4 ml vial was charged with 1 (1.24 mg, 0.16 μmol % based on the molar amount of di-n-butene), and a magnetic stirrer bar was added. Thereafter, 1.25 ml of the clear yellow stock solution and di-n-butene (315 μl, 2 mmol) were added with a syringe. The molar proportions based on the molar amount of di-n-butene are thus 0.04 mol % for Pd(acac)₂ and 0.6 mol % for PTSA. The vial was placed into a sample holder which was in turn inserted into a 300 ml Parr autoclave under an argon atmosphere. After the autoclave had been purged three times with nitrogen, the CO pressure was adjusted to 40 bar. The reaction proceeded at 120° C. for 20 hours. On conclusion of the reaction, the autoclave was cooled down to room temperature and cautiously decompressed. Isooctane was added as internal GC standard. Yield and regioselectivity were determined by means of GC. (MINO yield: 13%, n/iso regioselectivity: 59/41).

This experiment shows that the inventive ligand 1 forms a catalytically active palladium complex which catalyses the alkoxycarbonylation of di-n-butene. The structurally similar ligand 2, by contrast, is unsuitable for catalysing alkoxycarbonylation. 

1. Compound of formula (I)

where R¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₂₀)-heteroaryl radical; and R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl, —COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl, —CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl, —N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen.
 2. Compound according to claim 1, where at least two of the R¹, R², R³, R⁴ radicals are a —(C₃-C₂₀)-heteroaryl radical.
 3. Compound according to claim 1, where the R¹ and R³ radicals are each a —(C₃-C₂₀)-heteroaryl radical.
 4. Compound according to claim 1, where the R¹ and R³ radicals are each a —(C₃-C₂₀)-heteroaryl radical; and R² and R⁴ are each independently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C ₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl.
 5. Compound according to claim 1, where the R¹ and R³ radicals are each a —(C₃-C₂₀)-heteroaryl radical; and R² and R⁴ are each a —(C₁-C₁₂)-alkyl radical.
 6. Compound according to claim 1, where R¹, R², R³, R⁴, if they are a heteroaryl radical, are each independently selected from furyl, thienyl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, furazanyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidyl, pyrazinyl, benzofuranyl, indolyl, isoindolyl, benzimidazolyl, quinolyl, isoquinolyl.
 7. Compound according to claim 1, of the formula (1)


8. Complex comprising Pd and a compound according to claim
 1. 9. Process comprising the following process steps: a) initially charging an ethylenically unsaturated compound; b) adding a compound of formula (I)

where R¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₂₀)-heteroaryl radical; and R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)—heterocycloalkyl, —(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl, —COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl, —CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl, —N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen and a compound comprising Pd, or adding a complex according to claim 8; c) adding an alcohol; d) feeding in CO; e) heating the reaction mixture, with conversion of the ethylenically unsaturated compound to an ester.
 10. Process according to claim 9, wherein the ethylenically unsaturated compound comprises 2 to 30 carbon atoms and optionally one or more functional groups selected from carboxyl, thiocarboxyl, sulpho, sulphinyl, carboxylic anhydride, imide, carboxylic ester, sulphonic ester, carbamoyl, sulphamoyl, cyano, carbonyl, carbonothioyl, hydroxyl, sulphhydryl, amino, ether, thioether, aryl, heteroaryl or silyl groups and/or halogen substituents.
 11. Process according to claim 9, wherein the ethylenically unsaturated compound is selected from ethene, propene, 1-butene, cis- and/or trans-2-butene, isobutene, 1,3-butadiene, 1-pentene, cis- and/or trans-2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, hexene, tetramethylethylene, heptene, 1-octene, 2-octene, di-n-butene, and mixtures thereof.
 12. Process according to claim 9, wherein the ethylenically unsaturated compound comprises 6 to 22 carbon atoms.
 13. Process according to claim 9, wherein the compound comprising Pd in process step b) is selected from palladium dichloride, palladium(II) acetylacetonate, palladium(II) acetate, dichloro(1,5-cyclooctadiene)palladium(II), bis(dibenzylideneacetone)palladium, bis(acetonitrile)dichloropalladium(II), palladium(cinnamyl) dichloride.
 14. Process according to claim 9, wherein the alcohol in process step c) is selected from methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 2-propanol, tent-butanol, 3-pentanol, cyclohexanol, phenol, and mixtures thereof.
 15. A process for catalysis of an alkoxycarbonylation reaction, comprising: introducing a compound of formula (I)

where R^(l), R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₇₀)-heteroaryl radical; and R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently be substituted by one or more substituents selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl, —O—(C₁C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl, —COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl, —CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl, —N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen or a complex according to claim
 8. 